A new MAC address is learned when either:
* A packet is received from a new device on one of the ports of the switch with a new source address.
* The MAC address is added statically/dynamically/permanently to the CAM table via the CLI.
The following document describes how to collect Dynamic Content-Addressable Memory (CAM) entries for Catalyst switches using Simple Network Management Protocol (SNMP).
http://www.cisco.com/warp/public/477/SNMP/cam_snmp.html